Multiple video compression standards use entropy coding to efficiently express syntactic elements conveying the parameters of compression algorithms. Some of these models, e.g. context-adaptive binary arithmetic coding (CABAC) in H.264 and H.265, use adaptive models of the statistics of particular syntactic elements that evolve as successive values for each syntactic element are coded. At the start of coding a new coding region (picture, slice, tile) these models are typically initialized to a null state, and the statistical models in the encoder and the decoder are matched as they evolve.
Later video coding standards (e.g., H.265) can sub-divide a picture in two dimensions into coding regions called tiles, each coded independently of other tiles in the same picture. This enables encoding and decoding in parallel, for faster implementations, and also allows a two-dimensional (2D) sub-region to be more focused around video content within that region, than a one-dimensional (1D) subset of a raster scan of full picture width. In present schemes, the entropy model for a tile within a frame will begin at a common default and adapt as the coding within the tile proceeds.